In such a gas turbine engine known in the state of the art the gas duct or gas flow path is routed through a combustion section located between a compressor and a turbine section. The combustion section may include an annular array of combustors. High pressure air from the compressor flows through the combustion section where it is mixed with fuel and burned. As mentioned above, the combustors each comprise a burner for igniting the air/fuel mixture especially during start up of the gas turbine engine.
Combustion gases exit the combustion section to power the turbine section which drives the compressor. In single-shaft arrangements a high-pressure and a low-pressure turbine of the turbine section are mechanically connected and together drive an output power shaft. In twin-shaft arrangements a low-pressure turbine (power turbine) is mechanically independent, i.e. only drives the output power shaft, and a high-pressure turbine, or so called compressor turbine, drives the compressor. This combination acts as a gas generator for the low-pressure turbine. The combustion gases exit the turbine section through an exhaust duct.
A partial flame failure is defined as a flame failure in a subset of combustors, i.e. in one or more but not all combustors. Flame failure in all combustors would be considered a full flame failure. In case of such a partial flame failure, not all of the fuel supplied is burned in the combustion section, which leads to a suffering of the overall engine performance and efficiency. In the event of a partial flameout, fuel continues to be introduced by the control system into the combustion section in an attempt to meet demand. Adding fuel to a combustion section which is not completely burned has the adverse effect of producing a high level of emissions and unburned hydrocarbons. Moreover, this introduction of unburnt fuel into air produces an flammable mixture which could be ignited by any hot spot or spark and can lead to a subsequent explosion in the exhaust duct.
Various systems have been developed to detect partial flame failure conditions in a gas turbine engine. These systems include flame detection measurement systems which deploy infrared (IR) and ultraviolet (UV) sensors to detect the presence or absence of a flame at predetermined locations. This type of detection systems depends very much on the location of the sensors and can incorrectly identify absence of flame. Further, the flame detectors occasionally suffer the disadvantage of oil or smoke fouling, causing detection to fail. Moreover, these flame detection systems are generally expensive to supply and maintain.
GB 2 282 221 A describes a flame detector for a gas turbine engine. The flame detector comprises a first temperature sensor and a second temperature sensor which are both arranged to detect the ambient temperature outside the combustor. In addition, the second temperature sensor is arranged to also detect radiant heat from the combustion chamber. The first temperature sensor and the second temperature sensor are located in a first hollow member and a second hollow member, respectively. While the first hollow member is open towards an air stream the second hollow member is not only open towards the air stream but also towards a direction which allows a direct sight onto the flame in the combustion chamber through an aperture for introducing dilution air into the combustion chamber. Heat from the air streaming into the combustor chamber can be transferred convectively to both temperature sensors. In addition to the convective heat transfer, radiant heat from the flame inside the combustion chamber can be transferred to the second temperature sensor through the aperture. In case of successful ignition the flame within the combustion chamber generates radiant heat which can be sensed by the second temperature sensor but not by the first temperature sensor so that both temperature sensors measure different temperature values. In case ignition was not successful, both temperature sensors measure only heat transferred convectively from the air stream so that both measure the same temperature.
EP 1 637 805 A2 describes an ignition detecting method for a gas turbine. In this method, a variation of the temperature measured downstream of the turbine over time is used for judging whether ignition was successful.
U.S. Pat. No. 4,283,634 describes implementing a partial flameout detection method with a multi-shaft turbine.